Pulverizers for grinding different type materials are well known in the prior art. Coal is one such material wherein there exists a need to grind the material in order to render it suitable for use in certain applications. Fossil fuel fired power generation systems represent one such application in which it is desired to employ pulverized coal as the fuel. Such a system is commonly referred to as a coal fired power generation system.
For purposes of the discussion that follows, the coal fired power generation systems referred to above typically include the following major operating components: a coal feeder, an apparatus for pulverizing coal, a distribution system for distributing the pulverized coal, a furnace in which the pulverized coal is to be burned, and the requisite controls for effecting the proper operation of the coal fired power generation system. Of particular interest herein is the apparatus for pulverizing coal, which will often be referred to hereinbelow as a coal pulverizer. Coal pulverizers are not new. They have been known to exist in the prior art for more than half a century. Furthermore, many improvements have been made in the construction and/or mode of operation of coal pulverizers during this period. There are a number of features that it is advantageous for any coal pulverizer to possess, but particularly those which are designed for employment in a coal fired power generation system. Reference is had here to features such as reliability, low power consumption, minimum maintenance and a wide range of capacity. In addition, such a coal pulverizer advantageously should also be characterized by quiet operation, integrated lubrication systems, convenient adjustment and control of coal flow and fineness, and the ability to handle the high temperature air that is required for purposes of effecting therewith the drying to some degree of the high moisture coal that is to be pulverized in the coal pulverizer.
One particular type of conventional coal pulverizer is that which is commonly referred to in the industry as a bowl mill. Such a coal pulverizer obtains its name by virtue of the fact that the pulverization, i.e., grinding, of the coal, which takes place therein, is effected on a grinding surface that insofar as the configuration thereof is concerned bears a resemblance to a bowl. By way of exemplification and not limitation, reference may be had in this regard to U.S. Pat. No. 3,465,971, which issued Sep. 9, 1969 to J. F. Dalenberg et al., and/or U.S. Pat. No. 4,002,299, which issued Jan. 11, 1977 to C. J. Skalka, both of the latter patents being assigned to the same assignee as the instant application, for a teaching of the nature of the construction and the mode of operation of a prior art form of bowl mill that is suitable for use in a coal fired power generation system to effectuate the pulverization of the coal that is to be burned as fuel therein. As taught by the aforereferenced U.S. patents, a bowl mill essentially includes a body portion in which a grinding table is mounted for rotation, a plurality of grinding rollers that interact with the grinding table to effect the grinding of coal interposed therebetween, coal supply means for feeding to the interior of the bowl mill the coal that is to be pulverized therein, and air supply means for supplying to the interior of the bowl mill the air required for purposes of the operation of the bowl mill. In accordance with the mode of operation of such a bowl mill, the coal, which enters the bowl mill, is pulverized by virtue of the interaction of the grinding rollers with the grinding table. After being pulverized, the coal particles are thrown outwardly by centrifugal force, whereby the particles are fed into a stream of air that is made to enter the bowl mill. This stream of air, which now contains pulverized coal particles, flows through a tortuous path that is established in part by the positioning within the bowl mill of a suitably supported deflector means. As the stream of air and coal particles flows along the aforereferenced tortuous path, the sharp turns contained therein function to effect the separation of the coarse coal particles from the air stream. These coarse coal particles, which have been separated from the air stream, are then suitably returned to the grinding table for further pulverization, while the fine coal particles, which remain entrained in the air stream, are carried through the bowl mill in the air stream, and exit from the bowl mill along with the air stream.
Although bowl mills constructed in accordance with the teachings of the aforementioned U.S. patents have under actual operating conditions provided adequate performance, a need has nevertheless been evidenced for improvements to be made thereto. More specifically, prolonged operation of this type of bowl mill has revealed the existence of several undesirable conditions. One of these undesirable conditions is related to the need for and the manner in which a primary classification is had within the bowl mill of the material that is being pulverized. As employed herein the term primary classification is intended to refer to the separation of pulverized material from the air stream in which such material is entrained. In particular, reference is had here to that separation of pulverized material which occurs as a consequence of causing the air stream, within which the pulverized material is entrained, to follow a tortuous path through the bowl mill, whereby in the course of changing directions of flow as necessitated by the nature of this torturous path the larger of the particles of the pulverized material lose their momentum and are made to return to the surface of the grinding table whereat they are subjected to further pulverization.
In accordance with the teachings of the prior art, it has been known to employ a separator body liner design in a bowl mill for purposes of accomplishing the aforedescribed primary classification of pulverized material therewithin. In this regard, by way of exemplification and not limitation, such a bowl mill comprises the subject matter of U.S. Pat. No. 4,234,132, which issued on Nov. 18, 1980 and which is assigned to the same assignee as the present application. Although a bowl mill equipped with such a separator body liner design has proven to be adequate in terms of accomplishing the desired primary classification of the pulverized materials, disadvantages associated with the employment thereof have nevertheless been encountered, such as, including but not limited thereto, limited access to the internal workings of such a bowl mill due to the positioning of the deflector therein and the creation of undesirable wear distribution patterns within the interior of such a bowl mill.
To address these problems, the invention described in U.S. Pat. No. 4,523,721, which issued Jun. 18, 1985 to Theodore V. Maliszewski et al., and which is assigned to the same assignee as the instant application, and is incorporated herein in its entirety, was developed. In the Maliszewski et al. invention primary classification is had through the use of both a non-continuous vane wheel and an associated non-continuous deflector.
With reference to FIG. 1, the vane wheel 100 is supported on the periphery of a rotatable grinding table 14 of the bowl mill 10 by any suitable conventional form of fastening means, such as through the use of threaded fasteners 42. The vane wheel 100 is operative, when the air stream mixes with the coal particles as the air stream flows in surrounding relation to the grinding table 14, to cause the air steam to change direction and to flow counterclockwise to the direction of rotation of the grinding table 14. This in turn has the effect of causing pulverized material, which may be entrained in this air stream, to be carried in a direction, which is opposite to the direction of rotation of the grinding table 14, such that the larger of the particles of pulverized material lose their momentum, and separate from the air stream, and as a consequence thereof are returned to the surface of the grinding table 14 for additional pulverization.
As will be more fully described hereinafter, the non-continuous deflector 38 is mounted within the interior of the bowl mill 10 above and in spaced relation to the surface of the grinding table 14. The non-continuous deflector 38, as a consequence of being so mounted, is operative to cause the air stream, which has pulverized material entrained therein, to be directed toward the center of the interior of the bowl mill 10. This constitutes a change in the direction of flow of the air stream and is effective in causing the larger, i.e., heavier, particles of pulverized material, e.g., coal, entrained in the air stream to lose their momentum and to separate out of the air stream, and to thus be returned to the surface of the grinding table 14 for further pulverization.
The non-continuous deflector 38, as will be best understood with reference to FIG. 2, encompasses the following components: intermediate liner support plate 58, deflector liner support plate 60, intermediate liner 62, deflector liner 64 and deflector side liner 66a. Three such intermediate liner support plates 58 are preferably utilized, only one thereof, however, being visible in FIG. 2 of the drawing. The reason three intermediate support plates 58 are utilized is that the non-continuous deflector 38 is, as the name implies, not continuous around the interior of the bowl mill 10. Rather, the non-continuous deflector 38 is suitably provided with open areas that are located in juxtaposed relation to each of the three grinding journal openings/doors 205. Each of the intermediate liner support plates 58 is suitably located so as to be centered relative to a respective one of the grinding journal openings/doors 205.
The deflector liner support plates 60 are positioned such that the deflector liner support plates 60 occupy the area that extends between each pair of adjoining grinding journal openings/doors 205. Inasmuch as the bowl mill 10 is provided with three such grinding journal openings/doors 205, a like number, i.e., three such deflector liner support plates 60, are commonly employed in the bowl mill 10.
Each of the deflector liner support plates 60 has affixed thereto a deflector side liner. As best understood with reference to FIG. 2 of the drawings, each such deflector side liner is identified in FIG. 2 by the reference numeral 66a. In this regard, each such deflector side liner 66a is suitably positioned so that preferably the back edge thereof is flush with the interior surface of the separator body 12 and so that the bottom edge of each such deflector side liner 66a is arranged such as to be flush with the intermediate liner support plate 58, which has been previously described herein.
Each of the intermediate liner support plates 58, as best understood with reference to FIG. 2 of the drawings, has a multiplicity of intermediate liners 62 mounted thereon. To this end, these intermediate liners 62 are suitably positioned so as to be located below the grinding journal openings/doors 205. To complete the description of the non-continuous deflector 38, the non-continuous deflector 38 includes a bottom row of deflector liners 64 that is installed as a component thereof as well as a middle row of deflector liners 64 that is installed in mounted relation on the deflector liner support plates 60. In addition, there is also installed as a component of the non-continuous deflector 38 a top row of deflector liners 64.
While this design, as described hereinbefore in conjunction with the illustration thereof as depicted by way of exemplification and not limitation in FIGS. 1 and 2 of the drawings, has successfully enjoyed over twenty years of use, certain problems therewith have nevertheless arisen during this time. For example, it has been found that due to the vertical location at which the non-continuous deflector 38 is mounted above the grinding table 14 within the bowl mill 10, the liners 64, of which the non-continuous deflector 38 is comprised, are subjected to eroding due to these liners 64 being impinged upon by the coal that is entrained in the air stream. Accordingly, there exists a need for a new and improved primary classifier, which is capable of withstanding the erosion caused by the coal entrained in the air stream impinging thereagainst. Also, due to the vertical placement of the non-continuous deflector 38, as well as the volume of space occupied thereby, access to the interior of the bowl mill 10 for maintenance and repair purposes has been found to be somewhat limited. Accordingly, in addition there exists a need for a primary classifier design, which allows for greater access to the interior of a bowl mill.
Another problem associated with prior art designs of primary classifier results from the fact that the vane wheel 100 is not completely uniform around the entire perimeter of the bowl mill 10. Coupled with this is the fact that because of the sectioning of the vane wheel 100, the air streams with the coal entrained therein are channeled. Such channeling in turn produces high wear areas, as well as stratification of the coal flow. Such coal flow stratification reduces the efficiency that one is able to realize with the primary classifier. Accordingly, there also exists a need for a primary classifier in which there is no stratification of the coal flow.